The present invention relates generally to a removable cathode for an X-ray tube and more particularly to an indented cylindrical cathode having improved rigidity and a well-defined electron-emitting area.
The interchangeable cathode X-ray tube has been in use for nearly 50 years. The advantage of this tube is that the most fragile part, the cathode, may be replaced as it burns out without the expense of replacing the entire tube. However, these tubes have historically suffered from the disadvantage that the replaceable cathode must be very accurately aligned in order for the tube to achieve desired performance capabilities. This type of tube went out of favor when the cost of down-time due to alignment exceeded the cost of replacing the entire tube.
To overcome this disadvantage, this invention provides a rigid replaceable cathode for an X-ray tube which is designed to be firmly clamped into a prealigned holder in the X-ray tube.
A couple of prior patents have used structure which is superficially similar to that of the invention, although it does not and cannot perform the same function. U.S. Pat. No. 3,745,342 of Jan Le Poole shows a cathode assembly for an electron microscope utilizing a filament under tension which passes across two spaced V-blocks and through a cylindrical anode situated between the blocks. This patent relies on tension on the wire for mechanical stability and the use of grids in controlled potentials for bombardment heating of the wire. This structure does not have the required mechanical stability to allow easy, alignment-free replacement in an X-ray tube, nor does it have the necessary high-power capability necessary for X-ray tubes.
U.S. Pat. No. 4,100,449 of Robert Gange has a cylindrical filament which is substantially uniform in cross section about its longitudinal axis. While the physical construction of this low-power display cathode does provide mechanical strength as does this invention, Gange's invention lacks the unique thermodynamic and mechanical properties which enable it to be used for high-power X-ray applications.